Energy is described as the capacity for doing work and is the thing that makes things happen. Without energy, nothing in the universe would happen and whenever energy is used forces are involved in starting things, moving them or stopping them. Whilst there are different types of energy, most of it can be traced back to the Sun. In fact, more energy reaches the Earth from the Sun in an hour than to all of us in a year.
Chemical Energy: that part of the energy that is stored within an atom or molecule and is generally released by a chemical reaction. Radioactive materials release energy as they decay. Chemical energy is generally associated with food and fuels and is stored in the chemical make up of some substances such as plants, oil, coal and batteries. The chemical changes that take place produce new substances and provide energy. For example, when we eat food, energy is released when the food is digested.
Kinetic Energy: the energy a body possesses when it is in motion. All moving things therefore have kinetic energy, which increases as the mass and speed of the object also increases. If the mass of a moving object is doubled, then its kinetic energy is also doubled. If its speed doubles, then its kinetic energy is quadrupled.
Potential Energy: the energy that an object possesses due to its position or the state it is in. Types of potential energy include:
- Gravitational: a ball at the top of a slope has potential energy because it is gravity that pulls it down the slope. The potential energy of an object increases as its mass and height of fall increase.
- Elastic or strain: an elastic band or spring has elastic potential energy when they stretched or squashed.
- Electrical: a battery makes electrical energy from a chemical reaction and therefore has electrical potential energy. It is also described as the ability of an electric current to do work.
- Magnetic: a piece of iron near a magnet is said to have magnetic potential energy.
Heat: when a substance or object is heated the molecules in the material move, the hotter the material the faster the molecules move. The moving molecules possess kinetic energy that can be used to do work.
Energy is measured in joules after the English scientist James Joule, who realised that work produces heat and that heat is a form of energy. Work is done when a force moves an object through a measured distance. The formulae used to measure this is:
Work (in joules) = force (in newtons) x distance moved in the direction of the force (in metres).
Therefore one joule is the work done when a force of one newton moves something a distance of one metre in the direction of the force. Joules, and more especially kilojoules (kj), a thousand joules, are also used to measure the energy content of our food. The energy that is required to carry out work is released from fuel sources. A fuel is a substance that is used for producing heat or kinetic energy, either through the release of its chemical energy during burning or its nuclear energy by nuclear fission.